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<FONT color="green">001</FONT>    package gates;<a name="line.1"></a>
<FONT color="green">002</FONT>    <a name="line.2"></a>
<FONT color="green">003</FONT>    import exceptions.noQubitException;<a name="line.3"></a>
<FONT color="green">004</FONT>    import register.Register;<a name="line.4"></a>
<FONT color="green">005</FONT>    import gates.FunctionGate;<a name="line.5"></a>
<FONT color="green">006</FONT>    import mathtools.Complex;<a name="line.6"></a>
<FONT color="green">007</FONT>    /**<a name="line.7"></a>
<FONT color="green">008</FONT>     * Functional representation of a Cnot gate:<a name="line.8"></a>
<FONT color="green">009</FONT>     * This implements Gate interface, so consult this for public methods.<a name="line.9"></a>
<FONT color="green">010</FONT>     * The constructor for this gate is protected, so generating such an object is left<a name="line.10"></a>
<FONT color="green">011</FONT>     * for the factory class &lt;code&gt;Factory&lt;/code&gt;<a name="line.11"></a>
<FONT color="green">012</FONT>     * @author Jan Zaucha, James Hancox<a name="line.12"></a>
<FONT color="green">013</FONT>     *<a name="line.13"></a>
<FONT color="green">014</FONT>     */<a name="line.14"></a>
<FONT color="green">015</FONT>    public class CnotFunction extends FunctionGate {<a name="line.15"></a>
<FONT color="green">016</FONT>            <a name="line.16"></a>
<FONT color="green">017</FONT>            /** Store the target qubit the gate acts on*/   <a name="line.17"></a>
<FONT color="green">018</FONT>            private int target;<a name="line.18"></a>
<FONT color="green">019</FONT>            /** Store the control qubit the gate acts on*/  <a name="line.19"></a>
<FONT color="green">020</FONT>            private int ctrl;<a name="line.20"></a>
<FONT color="green">021</FONT>    <a name="line.21"></a>
<FONT color="green">022</FONT>    <a name="line.22"></a>
<FONT color="green">023</FONT>    <a name="line.23"></a>
<FONT color="green">024</FONT>            /**<a name="line.24"></a>
<FONT color="green">025</FONT>             * Protected constructor for a functional representation of a Cnot gate<a name="line.25"></a>
<FONT color="green">026</FONT>             * @param ctrl The Qubit in the Quantum register to act as the Control - decide if the target has to be changed.<a name="line.26"></a>
<FONT color="green">027</FONT>             * @param target The Qubit in the Quantum register to act as the Target - the Qubit that will change from 0 - 1.<a name="line.27"></a>
<FONT color="green">028</FONT>             */<a name="line.28"></a>
<FONT color="green">029</FONT>            protected CnotFunction(int ctrl, int target){<a name="line.29"></a>
<FONT color="green">030</FONT>                    if(ctrl==target){<a name="line.30"></a>
<FONT color="green">031</FONT>                            throw new IllegalArgumentException("ERROR: Cnot cannot be applied with equal Control and Target bits.");<a name="line.31"></a>
<FONT color="green">032</FONT>                    }<a name="line.32"></a>
<FONT color="green">033</FONT>                    this.target = target; <a name="line.33"></a>
<FONT color="green">034</FONT>                    this.ctrl = ctrl;<a name="line.34"></a>
<FONT color="green">035</FONT>            }<a name="line.35"></a>
<FONT color="green">036</FONT>    <a name="line.36"></a>
<FONT color="green">037</FONT>            /**<a name="line.37"></a>
<FONT color="green">038</FONT>             * Returns the name of the gate regardless of representation.<a name="line.38"></a>
<FONT color="green">039</FONT>             */<a name="line.39"></a>
<FONT color="green">040</FONT>            public String getName() {<a name="line.40"></a>
<FONT color="green">041</FONT>                    return "Cnot";<a name="line.41"></a>
<FONT color="green">042</FONT>            }<a name="line.42"></a>
<FONT color="green">043</FONT>    <a name="line.43"></a>
<FONT color="green">044</FONT>            /**<a name="line.44"></a>
<FONT color="green">045</FONT>             * Applies this gate to the given register. See interface &lt;code&gt;Gate&lt;/code&gt; for usage.<a name="line.45"></a>
<FONT color="green">046</FONT>             * @param r the register <a name="line.46"></a>
<FONT color="green">047</FONT>             */<a name="line.47"></a>
<FONT color="green">048</FONT>            public void apply(Register r) {<a name="line.48"></a>
<FONT color="green">049</FONT>                    if(r.getNumQbits()&lt;2){<a name="line.49"></a>
<FONT color="green">050</FONT>                            throw new noQubitException("ERROR: Cnot can only be applied to a Quantum Register with =&gt; 2 Quantum Bits.");<a name="line.50"></a>
<FONT color="green">051</FONT>                    }<a name="line.51"></a>
<FONT color="green">052</FONT>    <a name="line.52"></a>
<FONT color="green">053</FONT>                    if (target &gt;= r.getNumQbits() || target &lt; 0){<a name="line.53"></a>
<FONT color="green">054</FONT>                            throw new IllegalArgumentException("Target qubit not in register. Register size (qubits): " + r.getNumQbits() + " Target qubit: " + target);<a name="line.54"></a>
<FONT color="green">055</FONT>                    }<a name="line.55"></a>
<FONT color="green">056</FONT>    <a name="line.56"></a>
<FONT color="green">057</FONT>                    if (ctrl &gt;= r.getNumQbits() || ctrl &lt; 0){<a name="line.57"></a>
<FONT color="green">058</FONT>                            throw new IllegalArgumentException("Control qubit not in register. Register size (qubits): " + r.getNumQbits() + " Control qubit: " + ctrl);<a name="line.58"></a>
<FONT color="green">059</FONT>                    }<a name="line.59"></a>
<FONT color="green">060</FONT>                    int numStates = r.getHeight();    // number of states in register<a name="line.60"></a>
<FONT color="green">061</FONT>                    // create array to store updated register<a name="line.61"></a>
<FONT color="green">062</FONT>                    Complex [] newRegister = new Complex [numStates]; <a name="line.62"></a>
<FONT color="green">063</FONT>                    int this_Qstate;<a name="line.63"></a>
<FONT color="green">064</FONT>                    int this_Tstate;<a name="line.64"></a>
<FONT color="green">065</FONT>                    int numQubits = r.getNumQbits();<a name="line.65"></a>
<FONT color="green">066</FONT>                    // loop around whole register<a name="line.66"></a>
<FONT color="green">067</FONT>                    for(int i=0; i&lt;numStates; i++){<a name="line.67"></a>
<FONT color="green">068</FONT>                            // now shift right so that we have leftmost qubit the control qubit<a name="line.68"></a>
<FONT color="green">069</FONT>                            this_Qstate = i &gt;&gt; (numQubits - (ctrl +1));<a name="line.69"></a>
<FONT color="green">070</FONT>                            this_Tstate = i &gt;&gt; (numQubits - (target +1));<a name="line.70"></a>
<FONT color="green">071</FONT>    <a name="line.71"></a>
<FONT color="green">072</FONT>                            if(this_Qstate % 2 == 0){<a name="line.72"></a>
<FONT color="green">073</FONT>                                    // if get here don't flip<a name="line.73"></a>
<FONT color="green">074</FONT>                                    newRegister[i] = r.getElement(0, i);<a name="line.74"></a>
<FONT color="green">075</FONT>                            }<a name="line.75"></a>
<FONT color="green">076</FONT>                            else{<a name="line.76"></a>
<FONT color="green">077</FONT>                                    // else get 1 so flip<a name="line.77"></a>
<FONT color="green">078</FONT>                                    // we need to determine which state to flip with<a name="line.78"></a>
<FONT color="green">079</FONT>                                    if(this_Tstate % 2 == 0){<a name="line.79"></a>
<FONT color="green">080</FONT>                                            // if get here means that target for this state is 0 so flip to 1<a name="line.80"></a>
<FONT color="green">081</FONT>                                            newRegister[i] = r.getElement(0, i + (int)Math.pow(2, numQubits - (target +1) ));<a name="line.81"></a>
<FONT color="green">082</FONT>                                    <a name="line.82"></a>
<FONT color="green">083</FONT>                                    }<a name="line.83"></a>
<FONT color="green">084</FONT>                                    else{<a name="line.84"></a>
<FONT color="green">085</FONT>                                            // else get 1 so flip to 0<a name="line.85"></a>
<FONT color="green">086</FONT>                                            newRegister[i] = r.getElement(0, i - (int)Math.pow(2, numQubits - (target +1) ));<a name="line.86"></a>
<FONT color="green">087</FONT>                                    }<a name="line.87"></a>
<FONT color="green">088</FONT>                            }<a name="line.88"></a>
<FONT color="green">089</FONT>                    }<a name="line.89"></a>
<FONT color="green">090</FONT>                    <a name="line.90"></a>
<FONT color="green">091</FONT>                    r.update(newRegister);<a name="line.91"></a>
<FONT color="green">092</FONT>                    r.normalise();<a name="line.92"></a>
<FONT color="green">093</FONT>            }<a name="line.93"></a>
<FONT color="green">094</FONT>    <a name="line.94"></a>
<FONT color="green">095</FONT>    <a name="line.95"></a>
<FONT color="green">096</FONT>    <a name="line.96"></a>
<FONT color="green">097</FONT>    <a name="line.97"></a>
<FONT color="green">098</FONT>    }<a name="line.98"></a>




























































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